Not re-exporting learned OSPF routes

[Daryl Turner]

Hi,

Its true BIRD does not implement stub router advertisement as an
explicit feature, but you can manually set the cost of the stub links.

We have a similar need with a route reflector that needs to be kept
out of the forwarding path but needs its loopback advertised into
OSPF.

### OSPFv2 IPv4 ###
protocol ospf coreOSPF {
        table ospfT;
        area 0.0.0.0 {
                interface "em0", "em1" {
                        cost 65535;
                        type ptp;
                        hello 1; dead count 4;
                        authentication cryptographic;
                        password "secret password";
                };
                interface "lo1" { stub; };
        };
}


And here is an LSA from an upstream router showing the cost to use the
router to reach a remote network using the route reflector as transit.
It will only be used for forwarding after all other paths are down, at
which point you would be dropping traffic anyway.


    Link connected to: another Router (point-to-point)
     (Link ID) Neighboring Router ID: x.x.x.x
     (Link Data) Router Interface address: y.y.y.y
      Number of TOS metrics: 0
       TOS 0 Metrics: 65535


Hope that helps, seems to work for us without getting too complicated.
Daryl.


On 10 June 2013 10:11, Ondrej Zajicek <santiago at crfreenet.org> wrote:
> On Fri, Jun 07, 2013 at 08:07:59PM -0400, Ryan Whelan wrote:
>> I feel like this should be simple, but I can't find what I'm looking for...
>>
>> I have a few of routers spread across the country in a full mesh running
>> OSPF.  'Servers' and 'clients' connect to these 'routers' to connect to one
>> another- each 'server' and 'client' run a basic bird instance they use to
>> share a local address (X.X.X.X/32).  The issue is some of the 'servers'
>> connect to multiple 'routers' so if a link between 2 routers is down, OSPF
>> tries to route though a server... ('servers' don't have ip forwarding on)
>>
>> In short, how do I make sure the 'servers' can run bird to update OSPF with
>> their /32 address but not re-propagate routes they learn from OSPF (so as
>> to not be considered for route selection by the routers)?
>
> Hello
>
> OSPF works in a different way, there is no 're-propagation of routes' in
> OSPF, OSPF works by mapping network topology and then everyone
> calculates shortest paths. Every OSPF node is a part of a network
> topology and it is implicitly assumed to be a router. There is an
> extension that allows non-routing OSPF node to participate without
> acting as a transit node (RFC 3137), but this is not implemented in
> BIRD.
>
> There are some ways to solve your problem:
>
> 1) use OSPF only between routers and use a different protocol between
> servers/clients and routes.
>
> 2) use multiple OSPF instances (with different router ID) on servers,
> one instance for one link to a router, but there would be problems if
> you would need to share an iface between OSPF instances.
>
> --
> Elen sila lumenn' omentielvo
>
> Ondrej 'SanTiago' Zajicek (email: santiago at crfreenet.org)
> OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
> "To err is human -- to blame it on a computer is even more so."
>
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